The goal of the proposed research is to test the hypothesis that an unstable lipid, thromboxane A2, is involved in heart attacks and stroke. Thromboxane A2 will be produced biosynthetically and isolated by chromatography at -20 degree C. Tests will be carried out to establish its purity and the best conditions for storage will be determined. Its potency in inducing platelet aggregation and contracting arterial smooth muscle in vitro will be established. Experiments will be carried out to determine its effects on selected animals in vivo. The major plasma metabolite of thromboxane A2 will be detemined and isolated. A radioimmunoassay will be developed to measure the concentrations of this metabolite in the plasma of normal volunteers and those at high risk of thrombosis.